Author Topic: batteries in parallel (Read 6086 times)

benji · « **on:** May 19, 2008, 07:53:49 AM »

hey guys , i thought instead of using one big battery for high amps then why dont just connect 3 or 4 batteries in parallel?
i already have 4 nickel cadmium batteries which is 6 volts and 1 amps each , so connectin em in parallel i would get 6 volts 4 amps which is what i need
can this be done without any circuits? no danger? no battery charges another?

karlis · « **Reply #1 on:** May 19, 2008, 08:03:57 AM »

yes its posible, if thouse batteries are rechargable, you bether should find some good socket and maybe modify it so it would connect batteries parallel + to + and - to -

if you need more volts, then just put 2 in parallel and 2 in normal position ++ -- and other 2 +- +-

benji · « **Reply #2 on:** May 19, 2008, 08:18:18 AM »

i know batteries wont be 100% alike ,if one is 6.1 the other is 6.3 then the second would source current into the first,,right?

karlis · « **Reply #3 on:** May 19, 2008, 08:23:33 AM »

in your place i wont wory about that, your bot will have voltage regulator which will do the rest..

benji · « **Reply #4 on:** May 19, 2008, 08:31:24 AM »

actually regulators like 7805 and such wont handle 4 amps, and i want to feed servos directly from those batteries

dolinay · « **Reply #5 on:** May 19, 2008, 08:52:05 AM »

It should work. The batteries really should be as much the same as possible - the same type, capacity, age etc. And it will be better to charge them slowly (14 hours at 0.1 of the capacity, e.g. if you have battery 1000 mAh, charge at 100 mA). Or charge them separately.

If you combine batteries of different capacity then the one with smaller capacity will discharge sooner than the rest - and its voltage may drop too much, and also during charging it may get overcharged. But it's not harmful if you do not let the battery discharge too much and if you charge them slowly. Besides nickel cadmium batteries are very durable.

Things like this are used in radio controlled models. See for example here: http://www.redrockethobbies.com/RC_Airplane_Battery_Basics_s/263.htm

Anyway, it might be easier to use just 4 AA batteries (NiMh or NiCd) in a battery holder like on the picture. Such batteries can give 4 amps so you would not need any paralel connections.
http://www.radioshack.com/sm-battery-holders-and-clips--fi-2032264_cp-2032058.2032230.html

benji · « **Reply #6 on:** May 19, 2008, 09:05:46 AM »

this holder connects 4 AAs in seires , so each one should be able to provide 4 amps,, i dont find such,, i found ones which can provide 1 amps ,
so i need 4 holders to connect in parallel,,this makes my battery made of 16 cells ,,

dolinay · « **Reply #7 on:** May 19, 2008, 12:14:13 PM »

That's right, each battery would and could provide 4 apms. Check out this, for example:
http://www.batteryjunction.com/taapowermax-1800.html

It provides 18 Amps.
The max current depends on size (or capacity) but 1 amp is little for NiCd battery. The batteries in RC model trucks can discharge even at 20 C - that is 20 times their capacity, so for 1700 mAh battery that makes some 34 ams. Of course these are "heavy duty" ones, but if you buy regular NiMh batteries, AA size, 2500 mAh, for digital cameras, they should also have no problem providing 4 amps each as this is less than 2C for them.

benji · « **Reply #8 on:** May 19, 2008, 01:50:35 PM »

nice stuff, anyways i was talking about discharge current , i want it to be up to 4 amps,, ive read connectin batteries in parallel would increase the capacity but would it increase the discharge current too?

Nyx · « **Reply #9 on:** May 19, 2008, 02:13:01 PM »

Quote from: benji on May 19, 2008, 01:50:35 PM

nice stuff, anyways i was talking about discharge current , i want it to be up to 4 amps,, ive read connectin batteries in parallel would increase the capacity but would it increase the discharge current too?

No, it won't... But what do you want 4A for anyways?

benji · « **Reply #10 on:** May 19, 2008, 02:43:41 PM »

Quote

No, it won't...

why not? each packet has 1100 mamp discharge current, so wouldnt be able to provide 4 amps when its coneected in parallel?

Quote

But what do you want 4A for anyways?

a hexapod
which has 12 servos , 1 stepper , a sharp ir

dolinay · « **Reply #11 on:** May 20, 2008, 12:23:15 AM »

I am talking about discharge current too. Doesn't the page say "10C discharge max 18 AMP"?

The charge current is usually not over 1C but discharge current can be 10 or even 20 C. RC planes and truck typically use up the battery in some 5 to 10 minutes, then you charge it for about hour and can ride or fly again...

For sure connecting batteries in parallel lets you draw higher current from them. If one has max discharge 1 amp, 4 in parallel will have 4 amp max. That's correct, 100% sure, I fly with RC planes and helicopters a lot, use this a lot

Admin · « **Reply #12 on:** May 25, 2008, 02:45:59 PM »

http://www.societyofrobots.com/batteries.shtml

read where it says 'Notes on Parallel Batteries'

benji · « **Reply #13 on:** May 26, 2008, 06:12:10 AM »

well i says the batteries should be exactly the same... i baught 2 battreies,the same kind at the same time, the same properties
(6 volts nickel cadmium 1100mA)..
using a voltmeter it shows 6.1 volts the first one , 6.3 volts the second ,,

,what do i do?

gamefreak · « **Reply #14 on:** May 27, 2008, 07:25:27 PM »

Well i would think that if the batteries were the same as possible, but one had higher voltage, that they would level out, one would discharge while charging the other, in fact I would go so far as to say to batteries connected in parallel would constantly by oscillilating leading to a shorter shelf life because of resistance in the wire....

Commanderbob · « **Reply #15 on:** May 27, 2008, 09:59:00 PM »

You could probably just connect them. If you are worried about that then you could use diodes to prevent one battery from charging another but they you have to watch out for the voltage drop. You could also balance the cells by connecting them in parallel though a resistor and leave it like that over night. With 0.2V difference you should be fine. I say just connect them directly in parallel.

Speaking about parallel batteries is it safe to connect new non-rechargeable batteries in parallel?

Justin

benji · « **Reply #16 on:** May 28, 2008, 03:54:44 AM »

i dont htink the diode thing works,,theyre jus goin to find a way down in the circuit,, anyways
about that resistor,, looklike a nice idea but is it gonna work? would batteries act just like caps in this?

Quote

Speaking about parallel batteries is it safe to connect new non-rechargeable batteries in parallel?

why not

sdk32285 · « **Reply #17 on:** May 28, 2008, 07:06:22 AM »

Using schottky power diodes is probably the right approach. This will protect your batteries. Something to remember is that with the batteries in parallel your bus voltage will be what ever the highest battery is and you will primarily pull current from that battery. Also you probably need to heat sink those diodes.

benji · « **Reply #18 on:** May 28, 2008, 08:34:02 AM »

well i think you ur thinking to put a diode for each battery, anode at + and cathode to circuit then to battery - ,,right?
well
the shotcky diode would have a drop around 0.4 v so when there is the 6.3 battery then the voltage at its diode's cathode would be 6.3-0.4 = 5.9v
that means the voltage across the second diode would be 6.1 - 5.9 = 0.2 causing the diode to stay off so the 6.1 battery wont operate untill
the 6.3 battery becomes equal to 6.1
at that time the 6.3 battery should supply current alone to the whole circuit,, which is simply not possible

Admin · « **Reply #19 on:** May 30, 2008, 08:37:01 PM »

The method I do is fully charge both batteries seperately, then I connect them.

Commanderbob · « **Reply #20 on:** May 30, 2008, 10:40:19 PM »

Quote from: benji on May 28, 2008, 08:34:02 AM

at that time the 6.3 battery should supply current alone to the whole circuit,, which is simply not possible

Yes it is possible. When power is drawn above what the battery can produce then the voltage will drop. That allows the other batteries to kick in once the voltage is equal to theirs. For example if you short a battery with 3.6V then across the terminals you will get close to 0V but higher current. You can try this some time. Measure the voltage of a battery with and without a load.

Quote

Quote
Speaking about parallel batteries is it safe to connect new non-rechargeable batteries in parallel?
why not

If you connect them directly in parallel and they are not the same voltage one battery will attempt to charge the other and since they are not rechargeable this could be a problem. I just wanted to know if any one knows if this is safe or do you need diodes?

Thanks,
Justin

benji · « **Reply #21 on:** May 31, 2008, 02:44:12 AM »

Quote

Yes it is possible. When power is drawn above what the battery can produce then the voltage will drop. That allows the other batteries to kick in once the voltage is equal to theirs. For example if you short a battery with 3.6V then across the terminals you will get close to 0V but higher current. You can try this some time. Measure the voltage of a battery with and without a load.

mm sounds nice ,, but,, when the voltage drops before the second battery kicks in ,i guess that would cause the microcontroller to reset,, that could be a problem

Admin · « **Reply #22 on:** May 31, 2008, 06:44:59 AM »

Quote

If you connect them directly in parallel and they are not the same voltage one battery will attempt to charge the other and since they are not rechargeable this could be a problem. I just wanted to know if any one knows if this is safe or do you need diodes?

Charging non-rechargables can result in acid leaking

(although, I've seen 'non-rechargables' actually recharged)

As for the diode idea, I don't recommend it simply cause it reduces your useful voltage.

benji · « **Reply #23 on:** May 31, 2008, 08:55:23 AM »

Quote

As for the diode idea, I don't recommend it simply cause it reduces your useful voltage.

a shotcky diode would just drop a 0.4 volts ,,and you think i should just paralel them directly?
i was thinking if i connect them directly then the cuurent goin from one to the other to charge it would be very big cuz there is no resistor
,,wouldnt that damage anythin?

gamefreak · « **Reply #24 on:** May 31, 2008, 01:32:24 PM »

Quote from: Admin on May 31, 2008, 06:44:59 AM

Quote
If you connect them directly in parallel and they are not the same voltage one battery will attempt to charge the other and since they are not rechargeable this could be a problem. I just wanted to know if any one knows if this is safe or do you need diodes?
Charging non-rechargables can result in acid leaking
(although, I've seen 'non-rechargables' actually recharged)

As for the diode idea, I don't recommend it simply cause it reduces your useful voltage.

Speaking of acid leaks; My computer teacher/ robotics club mentor, had a lego RCX project for his programming class, me and my partner got ours, and attempted to turn it on. When it didnt naturally I checked the batteries, to my surprise, one battery was half encased in a whitish powder(resembled dried soap).

Another interesting story of battery acid: My dads car once suffered from its alarm randomly going off, it got really annoying at night. So one day we opened the hood and found one side of the battery fused to the connecter through acid.

So acid can cause power outage and power surges. odd....

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Author Topic: batteries in parallel (Read 6086 times)

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